Traditional manufacturing processes using powder metallurgy initially produce a near net shape part which is only 50–70% dense. These ‘green’ parts then undergo further processing to achieve full density and the desired mechanical properties. The densification is done either by lightly sintering and infiltrating with a lower melting temperature alloy or by a high temperature sintering alone. In the first method, the part's dimensional change is typically only ˜1% making it suitable for fairly large (˜0.5 m on a side) parts, but the resulting material composition will be a heterogeneous mixture of the powder material and the lower melting temperature infiltrant. Sintering the powder to full density will result in a homogeneous final material, but a part will undergo ˜15% linear shrinkage if it starts out at 60% density. For this reason, full density sintering is typically only used for smaller (<5 cm on a side) parts.
In many critical applications (structural, aerospace, military), a material of homogeneous composition is preferable because of certification issues, corrosion issues, machinability, or temperature limitations that might be imposed by the lower melting point infiltrant. Further, designers of metal components are not accustomed to working with composites of heterogeneous composition, and so this creates a psychological barrier.